The positive electrode current collectors in typical lithium ion batteries are aluminium foils. With the advancement of lithium ion battery technologies, lithium ion batteries with high energy density, light weight, and flexibility are desired. Light weight and improved energy density of the lithium ion batteries can be achieved by thinning the aluminum foil. However, due to the limitations from the manufacturing technology, the thickness of the aluminum foil can hardly be reduced (currently, the aluminum foil can be mass-produced at a thickness of 8 μm). Further, after the aluminum foil is thinned, the mechanical strength is reduced, resulting in a deteriorated processability. Therefore, there is a need for a new “thinning technique”.
In the prior art, aluminum is coated on a plastic (e.g., PET) and used as a current collector to increase the energy density, reduce the cost, and reduce the weight of the battery. However, the maximum thickness of the aluminum coating layer is up to 2.0 μm (where a thickness is needed to achieve a satisfactory conductivity), which is much larger than the thickness of an aluminum coating layer on a traditional packaging material. With increasing thickness of the coating layer, the aluminum coating layer becomes more prone to falling off from the plastic.
In addition, the surface of the aluminum foil needs to be protected from oxidation because the aluminum foil is in direct contact with the positive electrode material, and is corroded by the electrolyte solution after use for a long time, resulting in a reduced service life of the lithium ion battery. It is found that after aluminum is directly coated on a plastic, the aluminum coating layer may easily fall off if a conventional anti-oxidation method is used.